++ for this interesting observation. I guessed wrong at first because I thought the sub Bar would have had to have been prototyped as sub Bar() for it to get called in the last statement. Well, I was wrong there, but then I thought for sure if I prototyped it as sub Bar($), Perl would see that Bar alone is not a valid function call, so while examining the last statement it would try to interpret it as a package name instead. Nope, that gives a compile error.

My shot at an explanation: I'm guessing the -> operator will only do a method call when the left operand is either a bareword or a scalar (a package name or a ref). But since you have Bar defined as a sub in main's symbol table, it can never be a bareword, so it tries to evaluate it to a scalar: i.e., by calling the subroutine Bar. You end up with a scalar "Foo" which is a package name, so you get the package method call equivalent to Foo->new

I like this because now you can hijack stuff like this: 

Stealer.pm:

  package Stealer;
  use base 'Exporter';
  @EXPORT = qw/CGI/;

  sub CGI {
      return 'Stealer';
  }

  sub new {
      print "Stolen!";
  }

script.pl:

  use CGI;
  use Stealer;

  my $q = CGI->new;

[download]
Create a subclass of CGI without changing your CGI->method calls in the client code! Just import the CGI subroutine to the caller's namespace.

Update: In your code, if you wrap the declaration of the Bar subroutine in an eval q{...} block, the last line will compile "Bar" as a bareword string instead of a subroutine call, and the output will be "Bar's constructor called"

blokhead

In reply to Re: Capitalized subroutine names and packages by blokhead
in thread Capitalized subroutine names and packages by elusion

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.